An honorary flagpole stands at the site where 19 firefighters died battling an Arizona wildfire June 30 in Yarnell, Ariz.

YARNELL, Ariz. — Nineteen firefighters who died battling an Arizona wildfire became trapped by a wall of fast-moving flames as erratic winds whipped the blaze in all directions, pushing them back into a basin surrounded on three sides by boulder-strewn mountains, authorities speculated Tuesday during a tour of the site where the men were killed.

“It was like a blowtorch in a tunnel,” said Jim Paxon, a spokesman for the Arizona Division of Forestry, which was managing the fire around Yarnell, about 80 miles northwest of Phoenix. “The fire’s rate of speed and intensity was beyond comprehension.”

The fire began with a lightning strike Friday, June 28, and worsened by the hour through the weekend — at one point causing flames up to 20 feet high. The elite 20-member Granite Mountain Hotshot crew was called in on the morning of June 30 to help protect the former gold rush town in the foothills south of Prescott.

Afternoon thunderstorms and associated winds of more than 50 mph whipped the fire into an inferno as 19 of the Hotshots climbed over a ridge on the outskirts of town.

They likely saw the fire advancing on a nearby ranch, and were headed there to save the structure when the blaze suddenly turned toward them. The fire forced them to retreat to a relatively flat area surrounded by mountains where they found themselves trapped, said Prescott Wildland Fire Chief Darrell Willis, who helped form the Prescott-based team.

As the wall of flames advanced, the crew quickly worked to clear the area of scrub and brush that could fuel the fire, using hatchets, chain saws and shovels, hoping they could endure the intense heat as the blaze bore down, Willis said. They deployed their emergency shelters, but the heat was too much. All 19 died at the scene. The 20th crew member, who was serving as a lookout, was the only survivor.

The blaze ended up destroying more than 100 homes before it was fully contained on July 10.

On Tuesday, fire officials provided media a tour of the site where the men died, a somber return to a place where Willis described losing “19 adopted sons.”

“The heat was so intense their shelters broke down,” Willis said as he stood on the edge of the site, now encircled by a chain link fence. An American flag flapped in the wind above him, draped to a pole that has been placed there as a memorial to the men.

A Granite Mountain Hotshots T-shirt hangs on a charred cactus at the site. Fire officials asked that everyone touch it as they passed.

A ranch that was to serve as the Hotshot’s safety zone could be seen about 500 yards in the distance. Willis said the fire hooked around the men, blocking their way out of the fire’s path and backing them up to the mountains.

“They protected themselves as a last resort,” he said. “I don’t think they were aware of how quick” the fire was moving.

“This is the most extreme fire behavior I have ever witnessed,” Willis added.

A national team of investigators has finished gathering evidence from the scene and interviewing other firefighters. It’s expected their report on the fatalities will be completed sometime in late August or early September.